ALK and primary effusion lymphoma: Most B cell lymphomas express the B cell markers CD20, CD79a, and Pax 5, but occasionally one, two, or even all three markers are absent while there is genotypically a B cell neoplasia, especially anaplastic lymphoma kinase-positive DLBCL, PL, primary effusion lymphoma, and extracavitary human herpes virus 8 (HHV8)-positive DLBCL.